Most Recent Weekly Report: 4 March-10 March 2015

Based on reports from PVMBG, the Darwin VAAC reported that on 5 March an eruption at Sinabung generated a plume that rose 3 km above the summit. Satellite images detected an ash plume that rose to an altitude of 9.1 km (30,000 ft) a.s.l. and drifted 100-230 km WNW and NW. Later that day an ash plume rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted 75 km SW.

Most Recent Bulletin Report: January 2014 (BGVN 39:01)

The latest eruption of Sinabung volcano began mid-September 2013; activity through early December 2013 was reported in BGVN 38:09. This report describes the continuing eruption from December 2013 through April 2014, primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) and reports from the Darwin Volcanic Ash Advisory Centre (VAAC). Many videos and photographs also emerged online, some of outstanding information content.

Badan Nacional Penanggulangan Bencana (BNPB — the Indonesian National Agency for Disaster Management) produced a map in 2013 showing disaster-prone areas near Sinabung (figure 1 and table 1). Orange shading shows the highest hazard area, Area III. The S and SE extensions of Area III project downslope, delineating regions and villages with high exposure to pyroclastic- and lava-flow hazards.

Figure 1. 2013 hazard map of Sinabung showing villages within hazard-prone zones, including locations such as the village of Sukameriah located S of the summit (labeled 'Ds. Suka Meriah'). Table 1 translates critical portions of the map key. Courtesy of BNPB; from Carl (2014).

December 2013-January 2014. Based on webcam images, the Darwin VAAC reported that on 22 December an ash plume from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 55 km W. During 23-24 December ash plumes recorded by the webcam rose to an altitude of 3 km (10,000 ft) a.s.l.

PVMBG reported that seismicity at Sinabung increased during 21-26 December and indicated rising magma and lava-dome growth. Observers in Ndokum Siroga, about 8.5 km away, noted dense white plumes rising 70-1,200 m above the crater. Roaring was also periodically heard. A lava dome in the North Crater, visible on 24 December, was 56 m high and 210 m wide. During 25-26 December plumes were white and gray, and rose 300-400 m above the crater. On 26 December the lava-dome volume was estimated to be over 1 million cubic meters, with a growth rate of 3.5 cubic meters per second. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

On 30 December Badan Nacional Penanggulangan Bencana (BNPB) reported that the number of displaced people reached 19,126 (5,979 families). They also noted that activity at Sinabung had increased. Collapsing parts of the lava dome generated block-and-ash flows as well as pyroclastic flows which traveled as far as 3.5 km down the SE flank. Explosions and pyroclastic flows generated ash plumes that rose at least 6 km above the crater.

Figure 2. A woman carrying her daughter in an agricultural plot near Sinabung as an ash plume rose and pyroclastic flows descended the flanks on 4 January 2014. Photo by Ifansasti (2014).

At 1600 (UTC) (2300 local) on 4 January 2014, MODVOLC satellite thermal alerts were measured over Sinabung for the first time in at least the last 10 years. (The MODVOLC system was described in the 1980's and an online version started during 2000-2001, although some similar thermal databases now span on the order of 4 decades (Ramsey and Harris, 2011; Wright and others, 2004)). Lava effusion was high, resulting in thermal alerts during much of January 2014. From the time of that first alert, nearly daily to weekly alerts were measured through May 2014.

During 4-5 January pyroclastic flows were recorded 426 times. On 5 January the number of hybrid earthquakes increased, indicating lava-dome growth, and pyroclastic flows traveled 1.5-4.5 km SE. On 7 January ash plumes rose 1-6 km and drifted SW, and pyroclastic flows continued to travel 1.5-4.5 km SE. The village of Payang, ~4.6 km S of Sinabung's summit, was blanketed by ash on 7 January 2014 (figure 3).

Figure 3. The village of Payung (~4.6 km S of Sinabung's summit) as ash falls during the eruption of Sinabung on 7 January 2014. Image courtesy of Martin (2014); photography by Ulet Ifansasti/Getty Images.

A pyroclastic flow photographed on 10 January appears in figure 4. BNPB reported that the number of hybrid earthquakes decreased on 11 January and volcanic earthquakes increased. Amid these January eruptions aAsh plumes rose 1-5 km and drifted W, and pyroclastic flows traveled 1-4.5 km SE and 1 km E. Several villages in the Namanteran district reported ashfall. On 16 January, satellite imagery showed a white ash plume underlain by previous deposits of gray pyroclastic flows (figure 5). Around this time, the number of refugees reached over 22,000 persons.

Figure 4. Pyroclastic flows traveling down Sinabung's S flank during an eruption on 10 January 2014. This photo was taken from Berastepu village in Karo district (~4 km SE of volcano summit). Courtesy of Bracken (2014), with caption information from REUTERS/Beawiharta.

Figure 5. The Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite collected this natural-color image of an ash plume from Sinabung on 16 January 2014. Frequent collapses from the unstable lava dome at the volcano's summit created pyroclastic flows that have traveled at least 4.5 km down the volcano's flanks. The SE margin of these flows are just visible to the lower right of the plume. Courtesy of NASA Earth Observatory. Image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team. Caption by Robert Simmon.

A number of images of the eruption of Sinabung volcano during the second week of January 2014 are available on the Photovolcanica website (Roscoe, 2014). James Reynolds captured some remarkable videos of pyroclastic flows at Sinabung on 21 January 2014 (Earth Uncut TV, 2014; Vervaeck, 2014). Those videos showed explosions that often initiated the pyroclastic flows. As the flows moved downslope, they rapidly formed turbulent, ash-laden currents comprising the bulk of the flow volume (see Figure 3). An image of the S flank of Sinabung taken on 14 January shows lava flows erupting from the summit (figure 6).

Figure 6. Sinabung volcano on 14 January 2014 as it erupts a small plume and a lava flow that traveled down the volcano's S flank, as seen from Kuta Tengah village. Note the sinuous gulley (shaded depression) running downslope just to the right (E) of the lava flows; this is also a prominent landmark in figure 9. Courtesy of India Times (2014).

On 31 January 2014 Sinabung continued to effusively erupt viscous lava, further contributing to both the growth of the lava dome and the lava flow that descended the SE flank. The depression on the SE side of the volcano was mostly been filled by the lava flow, prompting concerns that pyroclastic flows lacked confinement and might take other paths to the S or E.

February 2014. On the morning of 1 February 2014 the lava dome collapsed and created one or two pyroclastic flows. As a result, 17 people (mostly students) died. All known fatalities occurred in Sukameriah village ('Ds. Suka Meriah,' figure 1). That village sits just over 3 km S of the summit, thus well within the 5-km-exclusionary zone. The resulting expanse of hot deposit generated a series of narrow spinning vortices ('twisters') of rising air and ash, that with height joined a rising plume (figure 7).

Waning trend. According to CVGHM, during 2-4 February 2014 no significant explosions or pyroclastic flows seemed to have occurred. Activity showed an overall decreasing trend. The number of seismic events related to the rise of new magma (hybrid earthquakes and tremor) had generally decreased over the preceding weeks. This corresponded to what was observed visually (when weather permitted clear views). Occasional medium-sized explosions and dome collapses produced pyroclastic flows that reached up to 3 km in length at 1350 on 3 February and at 0750 on 4 February.

Based on webcam images, Indonesian Met office notices, wind data, and ground reports, the Darwin VAAC reported that during 12-13 and 15-18 February ash plumes from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 25-95 km N, NE, and E.

During 15-23 February 2014 the eruption continued without significant changes, but with progressively decreasing activity. CVGHM noted the slow extrusion and gradual enlargement of the lava effusing from the summit vent and onto the S slope. Occasional rockfalls, ash emissions, and minor pyroclastic flows occurred as well. The erupted lava was determined to be andesite, typical of many stratovolcanoes in subduction settings.

March 2014. Based on wind data, webcam images, and satellite images, the Darwin VAAC reported that during 25 February-1 March and 3-4 March ash plumes from Sinabung rose to altitudes of 3-4 km a.s.l. and drifted 25-55 km E, NE, N, NW, W, and SW. Darwin VAAC also reported that during 4-7 and 9-11 March ash plumes from Sinabung rose to 3.7-4 km a.s.l. and drifted W and SW. During 6 and 9-11 March ash plumes drifted 35-165 km SW and W.

PVMBG described activity at Sinabung during 8-15 March based on observations from a post in the Ndokum Siroga village, 8.5 km away. Dense white plumes rose from the lava dome daily, as high as 1 km on most days; plumes rose 2 km on 12 March. Incandescent material originating from various parts of the lava dome traveled up to 2 km S and SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome increased. Sulfur dioxide emissions varied between 300 and 598 tons per day. Observations on 13 March showed that lava from the dome had flowed 2.4 km downslope.

On 15 March 2014, Sinabung was still at Alert Level 4 (the highest level). During 15-22 March 2014, there was a declining trend in the RSAM (real-time seismic amplitude measurement).

The volcano continued to be active on 18 March 2014 with no significant changes, but an overall decreasing trend. Lava effusion fed the S-flank lava lobe which had been mainly growing along its E side. No significant pyroclastic flows occurred, only frequent smaller rockfalls. Small ash plumes continued to be regularly visible on satellite imagery. The 18 March report indicated that seismicity decreased overall and hybrid earthquakes had disappeared. This suggested to the authors that pressure and magma supply rate had dropped significantly and that the eruption could be ending in the near future.

Based on webcam images, the Darwin VAAC reported that on 29 March an ash plume from Sinabung rose to an altitude of 4.3 km (14,000 ft) a.s.l. Meteorological cloud cover prevented satellite views.

On 30 March 2014, CVGHM reported a slowly decreasing trend in activity, with little variation over the preceding weeks. The viscous lava lobe remained weakly sustained and continued to grow very slowly. An intermittent steam and an occasional ash plume often rose to ~4.2 km a.s.l. No new pyroclastic flows occurred. During 23 March-8 April dense white plumes rose at most 1.2 km above the lava dome. Lava had traveled 2.5 km down the flanks as of 6 April and was incandescent at various locations. Incandescent material originating from the edges of the lava dome and flow traveled up to 2 km S and 500 m SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome decreased. Sulfur dioxide emissions varied but were relatively insignificant. Based on decreasing seismicity, deformation, and SO2 gas flux, CVGHM lowered the Sinabung Alert Level from 4 to 3 on 8 April 2014.

Flow paths into April 2014. Figure 8 shows two satellite images of Sinabung, the upper taken on 7 June 2013 (before the eruption) and the lower taken on 6 February 2014 (during the current eruption). The path of the pyroclastic and lava flows on the SE flank shows the extent of the devastated area and the orientation of other images (figures 6 and 9). Ashfall coated nearby villages and the flanks, as well as the coffee, chili pepper, and other types of plantations clustered at the foot of the volcano.

Figure 8. (Top) Pre-eruption Sinabung image acquired by Landsat on 7 June 2013; much of the surrounding landscape was covered by dark green forests. (Bottom) An image acquired on 6 February 2014 by the Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite. This is a natural-color image of an ash plume, a light gray apron of pyroclastic flow deposits, and broad scale ash fall coating much of the region. Frequent collapses from the unstable lava dome near Sinabung's summit created pyroclastic flows that traveled at least 4.5 km from the summit. NASA Earth Observatory images by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team and Landsat data from the U.S. Geological Survey. Caption by Robert Simmon and Adam Voiland.

CVGHM prepared an image (figure 9) of the path along which lava and pyroclastic flows traversed down the S side of Sinabung, delineating the extent of the lava flows at various dates from 31 January through 6 April 2014. On 6 April 2014 the lava flow was 2.5 km from the volcano summit. The image of 6 February 2014 (figure 8) revealed that pyroclastic flows had gone ~4 km from the summit of Sinabung. Some of those pyroclastic-flow deposits appear outboard and below the lavas at the bottom of figure 9.

Figure 9. This 6 April 2014 photograph of the S flank of Sinabung was annotated with dates by CVGHM (in Indonesian) to mark the advance of lava during 31 January-6 April 2014. The annotations include such features as flow margins and fronts ('lidah lava' means lava tongue). Taken from the CVGHM weekly report of 8 April 2014.

A report from CVGHM dated 10 April 2014 indicated that lava had recently extruded slowly, feeding a thick lobe on the S flank. The effusion rate had declined, hybrid earthquakes disappeared, and rockfall-induced seismicity decreased. Owing to these recent decreases in the intensity of activity, on 10 April authorities decreased the alert status from the Level 4 to 3 (on a scale of 1-4). People from some of the evacuated areas (to the E and NE) were allowed to return to their homes where they began the process of cleaning up the ash (of unstated thickness). Only the areas remaining off limits were within 3 km radius (eg., Sukameriah) and the SE sector village Berastapu (figure 1).

The lava lobe descending from the summit was considered by CVGHM to represent a large unstable mass draped onto the steep slope of the volcano. They acknowledged the risk of a sudden failure that could potentially result in a devastating pyroclastic flow. A pyroclastic flow did occur on 17 April 2014 at 1740, triggered by a partial collapse of the steep lava tongue. The flow was relatively small and only reached the then depopulated area at the base of the volcano.

Based on webcam images, satellite images, and wind data, the Darwin VAAC reported that on 22 April an ash plume rose to an altitude of 3.7 km and drifted almost 40 km W. MODVOLC thermal alerts were measured on 21 April 2014 at 1540 UTC and on 26 April 2014 at 1855 UTC.

Geophysical and geochemical plots. Figures 10 and 11 summarize measurements made and provided by CVGHM; figure 10 plots seismic signals measured from 7 November 2013 to 8 April 2014, and figure 11 plots various geochemical fluxes from1 September 2013 to 8 April 2014.

Figure 10. Plots showing on the y-axis the daily number ('jumlah') of various seismic events measured at Sinabung volcano for the period 7 November 2013 (07/11/2013) to 6 April 2014 (06/04/2014). The common x-axis values depict time, with dates shown for 10-day intervals, using the format 'dd/mm/yyyy'. The seismic types include: 'letusan'-seismically-detected eruptions; 'guguran'-avalanche signals, which correlated with the instability of the lava dome; 'hybrid' earthquakes—associated with growth of the lava dome; and 'VA'-deep volcanic earthquakes, indicating the persistence of a relatively small pressure due to intrusion of magma. Although not shown, CVGHM also measured low-frequency and shallow-volcanic earthquakes and tremor. Courtesy of CVGHM.

The deep volcanic ('VA') and hybrid earthquakes were among the earliest to show clear escalation, with the latter the most sustained. As seen on figure 10, all seismic data, except that associated with avalanches, decreased dramatically after mid-February 2014.

Figure 11 shows in the upper panel, the same seismic peak ('Letusan,' seismically detected eruptions) seen in the previous figure, an interval of high values measured in late December and especially prominent during early to mid-January. In the 2nd panel from the top, SO2 flux, there is a gap in data during the time of the eruption, due at least in part to the challenge of obtaining meaningful measurements in ash-choked plumes. Pronounced peaks occurred in available SO2 flux measurements during the periods 11-18 January and ~mid to late February 2014, with data gaps in their midst, probably for the same reasons just mentioned. Later and earlier measurements yielded much lower fluxes.

The 3rd panel down plots hot-spring-water temperatures ('suhu air panas'), which showed but gradual changes on the order of 0.5°C increase overall. The 4th and 5th panels down plot CO2 and H2S, respectively (in percent by volume) for the same area. Both those measurements display similar patterns. They lack data from January, around the time the eruption, thwarting direct comparisons to the eruption. In addition, CVGHM measured and reported deformation nearby Sinabung from tiltmeters and electronic distance measurement (EDM) equipment (not shown here). They also employ a webcam to monitor the volcano in clear weather.

Figure 11. Daily number of explosion earthquake ('Letusan') and various geochemical fluxes and concentrations measured at Sinabung volcano on a common x-axis scale for the period from 1 September 2013 to 8 April 2014 (in figure as 01/09/2013 to 08/04/2014; i.e., dates in the format 'dd/mm/yyyy'). The measurements indicated by the heading labels for each graph include: 'letusan' — eruption earthquakes per day; SO2 flux in tons/day; 'suhu air panas'—water temperature of the hot springs area in District Payung at the S foot of Sinabung in °C; and hot spring CO2 and H2S there in percent by volume. Courtesy of CVGHM.

Weekly Reports

4 March-10 March 2015

Based on reports from PVMBG, the Darwin VAAC reported that on 5 March an eruption at Sinabung generated a plume that rose 3 km above the summit. Satellite images detected an ash plume that rose to an altitude of 9.1 km (30,000 ft) a.s.l. and drifted 100-230 km WNW and NW. Later that day an ash plume rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted 75 km SW.

Based on satellite images and weather models, the Darwin VAAC reported that on 20 February an eruption from Sinabung generated ash plumes that rose to an altitude of 13.7 km (45,000 ft) a.s.l., drifted almost 540 km NW, and became detached. A lower-level eruption later that day produced an ash plume that rose to an altitude of 7.3 km (24,000 ft) a.s.l.

Based on satellite images, weather models, and ground observations, the Darwin VAAC reported that on 9 February an ash plume from Sinabung rose to an altitude of 4 km (13,000 ft) a.s.l. and drifted 10-30 km W.

Based on satellite images and weather models, the Darwin VAAC reported that on 15 January an ash plume from Sinabung rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted over 45 km NW. On 18 January BNPB reported that activity at Sinabung remained high; low-frequency earthquakes and constant tremor were detected. A pyroclastic flow traveled 2 km S and ash plumes rose 700 m. The number of people that remained displaced was 2,443 (795 families). The Alert Level was at 3 (on a scale of 1-4).

Based on satellite images, weather models, and ground observations, the Darwin VAAC reported an eruption from Sinabung on 10 January with an ash plume that rose to an altitude of 4 km (13,000 ft) a.s.l. Ashfall was reported in nearby areas at night on 11 January. During 12-13 January ash plumes rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted E.

BNPB reported that an eruption at Sinabung occurred during 0833-0919 on 3 January; this event was larger than the events that had been occurring almost daily. Pyroclastic flows traveled 2-4 km down the flanks and ash plumes rose as high as 3 km. Ashfall was reported in Payung (5 km SSW), Tiganderket (7 km W), Selandi (5 km SSW), Juhar (20 km SW), and Laubaleng (35 km WSW). Since the September 2013 onset of activity, 2,443 people (795 families) still remained displaced.

PVMBG reported that 53 pyroclastic flows at Sinabung occurred during 8-16 December and traveled as far as 4.5 km S and 1 km SE. Ash plumes rose as high as 5 km and drifted W and SW. Since October a new lava dome had grown from the crater (on the W side of the lava tongue) and was 215 m long. The main lava tongue was about 2,947 m on 15 December. The Alert Level remained at 3 (on a scale of 1-4).

Based on webcam views and weather models, the Darwin VAAC reported that on 10 December an ash plume from Sinabung rose to an altitude of 4.9 km (16,000 ft) a.s.l. and drifted SW. The notice stated that the eruption was more significant and higher than the intermittent pyroclastic flows observed during the previous week. Eruptions during 11-16 December produced ash plumes that rose to altitudes of 4.3-6.1 km (14,000-20,000 ft) a.s.l. and drifted at most 30 km N, NW, and W.

Based on webcam views and weather models, the Darwin VAAC reported that on 3 December an ash plume from Sinabung rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted E. Eruptions during 5-7 December produced ash plumes that drifted 2-20 km in multiple directions. On 14 December an ash plume rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted W.

Based on webcam views and weather models, the Darwin VAAC reported that duirng 19-20 November eruptions from Sinabung produced ash plumes that rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted W. Continuous dense white plumes and intermittent pyroclastic flows were also visible. During 22-23 November intermittent pyroclastic flows recorded by the webcam reached the base of the volcano. On 23 November an ash plume rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted S.

On 14 November BNPB reported that activity at Sinabung remained elevated; avalanches occurred 79 times, and pyroclastic flows generated by three of the avalanches traveled 4 km S. Ash plumes rose 1 km and the lava flow was active 500 m down from the crater on the S and W flanks. The report stated that 2,986 people from 956 households remained displaced. The Darwin VAAC reported that ash plumes drifting W, SW, and S were recorded by a webcam during 12-18 November. Dense white plumes and intermittent pyroclastic flows were visible on 19 November.

The Darwin VAAC reported that eruptions from Sinabung were recorded by a webcam during 4-7 and 10-11 November. Based on a report from PVMBG, the VAAC reported that an eruption on 9 November produced an ash plume that rose to altitudes of 3-3.7 km (10,000-12,000 ft) a.s.l. and drifted over 35 km NW.

Based on a pilot observation, the Darwin VAAC reported localized ash from Sinabung on 2 November, but a meteorological cloud in the area prevented further observations. A pyroclastic flow and an ash plume were recorded by the webcam on 3 November. The ash plume rose to an estimated altitude of 4.6 km (15,000 ft) a.s.l. and drifted NE; the altitude of the ash plume was again uncertain due to meteorological cloud. On 4 November an ash plume observed with the webcam rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted N.

Based on webcam views, wind data models, and satellite images, the Darwin VAAC reported that during 23-27 October ash plumes rose from Sinabung. During 23-24 October ash plumes drifted 15-40 km N and SW. A small eruption observed on the webcam on 25 October produced a minor amount of ash that drifted SW; a later ash plume drifted almost 30 km WNW. The next day another eruption generated an ash plume that drifted E. Ash emissions on 27 October were recorded by the webcam. The VAAC noted that PVMBG reported an ash plume that rose to an altitude of 5.5 km (18,000 ft) a.s.l. and then dissipated.

On 27 October BNPB reported that activity at Sinabung remained high; on 26 October pyroclastic flows traveled 3.5 km S and avalanches occurred multiple times. Hot ash clouds rose 2 km. The report stated that 3,284 people from 1,018 families remained in evacuation shelters.

Based on webcam views and wind data models, the Darwin VAAC reported that during 15-20 October daily small eruptions from Sinabung generated ash plumes that rose to an altitude of 4.3 km (14,000 ft) a.s.l. The plumes drifted 55 km NW during 15-17 October and ESE on 19 October.

The Darwin VAAC reported that an eruption from Sinabung, observed in the webcam at 1248 on 8 October, generated a pyroclastic flow. An ash plume rose to an altitude of 4.9 km (16,000 ft) a.s.l. (based on webcam views and wind models) and drifted E. Eruptions recorded at 0636 and 1107 on 9 October generated ash plumes that rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted NE, based on webcam views and wind models. On 10 October satellite images and the webcam detected an ash plume drifting 55 km NE. An ash plume drifting SW at an altitude of 3 km (10,000 ft) a.s.l. was recorded by the webcam on 11 October. On 14 October an ash plume was again recorded by the webcam and rose to an altitude of 4 km (13,000 ft) a.s.l. and drifted SW.

Based on reports from PVMBG, BNPB reported four eruptions from Sinabung on 5 October. The first one occurred at 0146, and produced a pyroclastic flow that traveled 4.5 km S and an ash plume that rose 2 km. The next three events, at 0638, 0736, and 0753, all generated pyroclastic flows that traveled 2.5-4.5 km S. The fourth event also produced an ash plume that rose 3 km. A news article stated that pyroclastic flows from a fifth event at 0900 were smaller, but again traveled 4.5 km after a sixth event at 1200.

According to the Darwin VAAC a low-level eruption recorded by the PVMBG webcam generated a pyroclastic flow on 6 October; some of the ash rose higher and drifted E. The Jakarta MWO noted that an ash plume rose to an altitude of 5.2 km (17,000 ft) a.s.l. and drifted S on 7 October. Cloud cover prevented satellite observations. A news article posted on 8 October noted that eruptions in the previous four days caused some evacuations.

According to news articles a pyroclastic flow at Sinabung traveled 2 km SE down the flanks at 1343 on 24 September. The height of a corresponding ash plume could not be determined because it rose into the cloud cover. About 4,700 people remained in evacuation shelters. On 30 September at 1720 an ash plume rose 2 km and a pyroclastic flow traveled 3.5 km.

PVMBG reported that RSAM values from Sinabung were low and stable during 12-20 September. Earthquake signals indicating lava-dome instability were recorded and had increased from 96 to 110 events/day since the 5-11 September period. Seismicity also continued to signify growth of the main lava flow on the flanks; incandescent lava was visible at the top, middle, and front of the lava flow. The length of the lava flow was 2.9 km on 6 September. White and sometimes bluish plumes rose as high as 1 km above the lava dome. Pyroclastic flows traveled 2.5 km SE on 15 September and 2 km S on 18 September. The Alert Level remained at 3 (on a scale of 1-4).

CVGHM reported a white plume that was occasionally brown and blue reaching 100-2,000 m above Sinabung’s crater during 8-14 July. Pyroclastic flows were observed on 10 and 12 July from the W side of the crater. On 10 July, the hot flows reached a maximum of 3 km S while the flows on 12 July extended 3-4 km S. A spokesman from the national disaster management agency noted that hot ashfall occurred in several places around the Karo district, but did not merit further evacuations. CVGHM reported that SO2 emissions were measured once during 8-14 July and yielded 1,252 tonnes/day; during the elevated activity of 11-18 January 2014 values were as high as 3,796 tonnes/day. The Alert Level remained at 3 (on a scale of 1-4).

After more than a month of dome growth and lava flows, PVMBG reported that Sinabung erupted explosively again on 29 June. The eruption plume rose to 4 km (13,000 ft) a.s.l. and pyroclastic flows extended 4.5 km SE. Visual observations were impeded by inclement weather. About 14,000 persons remain evacuated since September 2013. The Alert Level remains at 3 (on a scale of 1-4).

PVMBG reported visual monitoring of Sinabung during 1-17 June from the Ndokum Siroga village (~8.5 km of the summit). Dome growth continued and was accompanied by a lava flow that was frequently visibly incandescent. The observatory noted that the lava flow (particularly avalanches from the flow front) presented a threat to areas S and SE within a 5 km radius from the summit. During this reporting period, seismicity was dominated by tremor associated with avalanches, and there was minor deformation. Alert Level 3 was maintained (on a scale of 1-4).

Based on webcam images, satellite images, and wind data, the Darwin VAAC reported that on 22 April an ash plume from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted almost 40 km W.

PVMBG described activity at Sinabung during 23 March-8 April based on observations from a post in the Ndokum Siroga village, 8.5 km away. Dense white plumes rose at most 1.2 km above the lava dome. Lava had traveled 2.5 km down the flanks as of 6 April and was incandescent at various locations. Incandescent material originating from the edges of the lava dome and flow traveled up to 2 km S and 500 m SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome decreased. Sulfur dioxide emissions varied but were relatively insignificant. The Alert Level was lowered to 3 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km on the S and SE flanks, and 3 km in the other directions.

Based on webcam images, the Darwin VAAC reported that on 29 March an ash plume from Sinabung rose to an altitude of 4.3 km (14,000 ft) a.s.l. Meteorological cloud cover prevented satellite views. Gas emissions were noted on 30 March.

PVMBG described activity at Sinabung during 15-22 March based on observations from a post in the Ndokum Siroga village, 8.5 km away. Dense white plumes rose 500 m above the lava dome daily, and as high as 1 km on 21 March. Lava had traveled 2.4 km down the flanks as of 20 March and was incandescent at various areas. Incandescent material originating from the edges of the lava dome and flow traveled up to 1.5 km S and 200 m SE. A pyroclastic flow traveled 3 km S on 17 March. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome decreased slightly. Sulfur dioxide emissions varied between 300 and 598 tons per day, indicating no new magma. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

PVMBG described activity at Sinabung during 8-15 March based on observations from a post in the Ndokum Siroga village, 8.5 km away. Dense white plumes rose from the lava dome daily, as high as 1 km on most days; plumes rose 2 km on 12 March. Incandescent material originating from various parts of the lava dome traveled up to 2 km S and SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome increased. Sulfur dioxide emissions varied between 300 and 598 tons per day. Observations on 13 March showed that lava from the dome had flowed 2.4 km downslope. The report also noted that three people burned during a pyroclastic flow on 1 February later died in the hospital bringing the total number of casualties from that day to 17. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

Based on wind data, satellite images, and webcam images, the Darwin VAAC reported that during 4-7 and 9-11 March ash plumes from Sinabung rose to altitudes of 3.7-4 km (12,000-13,000 ft) a.s.l. and drifted W and SW. Ash plumes drifted 35-165 km SW and W during 6 and 9-11 March.

On 19 February BNPB reported that villagers outside of the 5-km evacuation zone around Sinabung continued to return to their homes. Based on wind data and satellite images, the Darwin VAAC reported that during 19 and 21-22 February ash plumes rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted 25-35 km NE and SW. Ash plumes were visible in webcam images during 23-25 February; ash plumes rose to altitudes of 3.7-4.6 km (12,000-15,000 ft) a.s.l. on 25 February and drifted 45 km E. On 24 February BNPB noted that 16,361 people remained in 34 evacuation shelters. Dense white plumes rose 100-300 m above the dome and incandescent material as far as 2 km SE from the dome was observed.

Based on webcam images, Indonesian Met office notices, wind data, and ground reports, the Darwin VAAC reported that during 12-13 and 15-18 February ash plumes from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 25-95 km N, NE, and E. On 16 February BNPB reported that villagers outside of the 5-km evacuation zone around Sinabung continued to return to their homes.

Based on reports from PVMBG, BNPB reported on 8 and 9 February that seismicity at Sinabung continued to be dominated by hybrid earthquakes, indicating pressure below the crater and a growing lava dome. Earthquakes associated with avalanches increased. The 9 February report noted that the number of displaced people reached 32,351 (9,991 families) in 42 evacuation centers. Refugees from 17 villages outside the 5-km radius were allowed to return to their homes, starting with four villages during the first phase.

PVMBG described activity at Sinabung during 24-31 January based on observations from a post in the Ndokum Siroga village, 8.5 km away. On 24 January dense white plumes rose as high as 1 km. During 25-26 and 28-31 January dense grayish-white plumes rose 0.1-1.5 km; on 27 January plumes rose 4 km. Each day pyroclastic flows traveled 0.5-4.5 km SE and S. Incandescent material was observed 0.2-1.5 km SE of the vent. Seismicity remained high, with constant tremor, hybrid earthquakes indicating a growing lava dome, and volcanic earthquakes. The number of low-frequency earthquakes continued to decrease. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

Badan Nacional Penanggulangan Bencana (BNPB) reported on 31 January that since activity at Sinabung had not increased residents from 16 villages outside of the 5-km radius were allowed to return to their homes. At 1030 on 1 February a large dome collapse generated pyroclastic flows that traveled 4.5 km S, killing 15 and injuring two people that had entered the 5-km exclusion zone without permission. On 4 February the number of displaced people reached 31,739 (9,915 families) in 42 evacuation centers, many from outside of the exclusion zone.

PVMBG described activity at Sinabung during 10-17 January based on observations from a post in the Ndokum Siroga village, 8.5 km away. Each day brownish white or gray and white ash plumes rose as high as 5 km, pyroclastic flows traveled 0.5-4.5 km E, SE, and S, and incandescent material was observed on the S and SE flanks as far as 3 km. Seismicity remained high, with constant tremor, hybrid earthquakes indicating a growing lava dome, and volcanic earthquakes. The number of low-frequency earthquakes continued to drop, however. The Alert Level remained at 4 (on a scale of 1-4).

PVMBG described activity at Sinabung during 3-10 January based on observations from a post in the Ndokum Siroga village, 8.5 km away. Each day ash plumes rose as high as 5 km, pyroclastic flows traveled 0.5-4.5 km E, SE, and S, and incandescent material was observed as far as 2 km SE and E. Roaring was periodically heard and burned trees on the S flank were noted on 4 January. Seismicity remained high, with constant tremor, hybrid earthquakes indicating a growing lava dome, and volcanic earthquakes. The number of low-frequency earthquakes dropped dramatically, however. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 7 km on the SE flank and 5 km elsewhere. Badan Nacional Penanggulangan Bencana (BNPB) reported that the number of hybrid earthquakes decreased on 11 January and volcanic earthquakes increased. Ash plumes rose 1-5 km and drifted W, and pyroclastic flows traveled 1-4.5 km SE and 1 km E. Several villages in the Namanteran district reported ashfall. The 11 January report noted that the number of displaced people reached 25,516 (7,898 families) in 38 evacuation centers.

Badan Nacional Penanggulangan Bencana (BNPB) reported that during 30-31 December 2013 Sinabung continued to be very active. Ash plumes rose as high as 7 km above the lava dome, pyroclastic flows traveled as far as 3.5 km SE, and incandescent avalanches traveled 1.5 km SE. On 3 January the lava dome continued to grow and collapse. Pyroclastic flows occurred 172 times and traveled 2-4 km SE, and ash plumes rose 2-6 km. Two villages located 6.5 km SE, Jerawa and Desa Pintu Besi, were evacuated. On 4 January pyroclastic flows were larger and more frequent. They continued to travel up to 5 km SE as well as 3.5 km SSE. Ash plumes rose 2-4 km. On 5 January the number of hybrid earthquakes increased, indicating a growing lava dome, and pyroclastic flows traveled 1.5-4.5 km SE. During 4-5 January pyroclastic flows were recorded 426 times. On 7 January ash plumes rose 1-6 km and drifted SW, and pyroclastic flows continued to travel 1.5-4.5 km SE. The number of refugees reached 22,145.

PVMBG reported that seismicity at Sinabung increased during 21-26 December and indicated rising magma and lava-dome growth. Observers in Ndokum Siroga, about 8.5 km away, noted dense white plumes rising 70-1,200 m above the crater. Roaring was also periodically heard. A lava dome in the North Crater, visible on 24 December, was 56 m high and 210 m wide. During 25-26 December plumes were white and gray, and rose 300-400 m above the crater. On 26 December the lava-dome volume was estimated to be over 1 million cubic meters, with a growth rate of 3.5 cubic meters per second. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

On 30 December Badan Nacional Penanggulangan Bencana (BNPB) reported that the number of displaced people reached 19,126 (5, 979 families). They also noted that activity at Sinabung had increased. Collapsing parts of the lava dome generated block-and-ash flows as well as pyroclastic flows which traveled as far as 3.5 km down the SE flank. Explosions and pyroclastic flows generated ash plumes that rose at least 6 km above the crater.

Based on webcam images, the Darwin VAAC reported that on 22 December an ash plume from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 55 km W. During 23-24 December ash plumes recorded by the webcam rose to an altitude of 3 km (10,000 ft) a.s.l.

PVMBG reported that observers in Ndokum Siroga, about 8.5 km away, noted gray plumes rising 1 km above Sinabung on 6 December. Grayish-white plumes rose as high as 400 m on 7 December, and dense white plumes also rose as high as 400 m the next day. Dense grayish-to-white plumes rose 70-200 m on 9 December. White plumes rose 100-150 m above the crater during 10-13 December. Tremor during 6-13 December was recorded continuously, with varying amplitude. The number of low-frequency earthquakes significantly increased on 7 December, and the number of hybrid earthquakes increased the next day. RSAM values had steadily increased since 28 November. The Alert Level remained at 4 (on a scale of 1-4).

Based on webcam data, wind data, satellite image analysis, and PVMBG, the Darwin VAAC reported that on 4 December an ash plume from Sinabung rose to an altitude of 8.2 km (27,000 ft) a.s.l. and drifted N. Later that day and during 5-6 December ash plumes rose to altitudes of 3-3.7 km (7,000-12,000 ft) a.s.l. and drifted NW. On 10 December an ash plume rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted 75 km NW. A few hours later an ash plume rose to an altitude of 11.6 km (38,000 ft) a.s.l. and drifted over 90 km NW.

Based on webcam data and wind data, the Darwin VAAC reported that during 28-31 November and 2 December ash plumes from Sinabung rose to altitudes of 3-5.5 km (10,000-18,000 ft) a.s.l. Ash plumes drifted 150 km W during 30-31 November and 55 km Won 2 December. On 3 December ash plumes rose to an altitude of 8.2 km (27,000 ft) a.s.l. and drifted W. According to a news report on 2 December, landslides killed nine people in the Gundaling village, 12 km E.

PVMBG reported three explosions from Sinabung on 17 November. The first explosion, at 2024, generated an ash plume that rose 500 m and drifted SW, and a pyroclastic flow that traveled 500 m down the SE flank. At 2152 a dense ash plume from an explosion rose 500 m and drifted SW. Incandescent material was ejected 50 m away from the crater. At 2252 an ash plume rose 1 km and drifted SW. At 0704 on 18 November an explosion generated an ash plume that rose 8 km and drifted SW. A pyroclastic flow also traveled 800 m down the SE flank.

On 19 November at 2155 a dense ash plume rose 10 km, drifted SW, and exhibited lightning. Pyroclastic flows again traveled 500 m SE. Multiple explosions on 20 November (at 0240, 0405, 0529, 0619, and 0641) generated ash plumes that rose to heights between 1 and 3.5 km. An explosion at 1716 was detected by the seismic network but cloud cover prevented observations of possible plumes. White plumes rose 100 m on 21 and 23 November; misty conditions prevented visual observations on 22 November. On 23 November scoria fell in the Sigarang-garang and Desa Kuta villages in the NNE. Two explosions on 24 November, at 0043 and 0232, were detected but not visually observed. Ash plumes rose 8 km and drifted NNE at 0727, rose 1 km at 0812, and rose 3 km at 0855. Since Sinabung's activity continued to increase, PVMBG raised the Alert Level to 4 (on a scale of 1-4) on 24 November. PVMBG noted that residents and tourists were not to approach the crater within a 5-km radius, and that remaining residents in 17 villages around the volcano were to be evacuated. On 25 November Badan Nacional Penanggulangan Bencana (BNPB) reported that 17,713 people, out of the 20,270 residents living within 5 km, had been evacuated to 31 shelters.

Based on webcam data and satellite images, the Darwin VAAC reported that during 13-14 November an ash plume from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted almost 150 km NW and W. According to a news article, a pyroclastic flow traveled 1.2 km down the SE flank on 14 November, prompting more evacuations from villages near the base of the volcano. The article noted that more than 7,000 people had been evacuated from 10 villages.

An explosion observed with the webcam on 18 November produced an ash plume that rose to an altitude of 7.6 km (25,000 ft) a.s.l. About 30 minutes later an ash plume also visible in satellite images rose to an altitude of 11.3 km (37,000 ft) a.s.l. and drifted 65 km W. Four hours later satellite images showed ash plumes at an altitude of 9.1 km (30,000 ft) a.s.l. to the W of Sinabung and at an altitude of 4.6 km (15,000 ft) a.s.l. over the crater. On 19 November the webcam recorded an ash plume that rose to an altitude of 4.6 km (15,000 ft) a.s.l. over the crater. A news article stated that later that night that an ash plume rose to an altitude of 10 km (32,800 ft) a.s.l.

A news article from 20 November noted that volcanologists updated the hazard map for Sinabung. The second-tier disaster-prone area, previously defined as a radius of 2-3 km from Sinabung’s crater, was expanded to 4-5 km.

Based on information from the Jakarta Meteorological Watch Office, webcam data, wind data, and satellite images, the Darwin VAAC reported that on 6 November an ash plume from Sinabung rose to an altitude of 3 km (10,000 ft) a.s.l. The next day an ash plume rose to the same altitude but was not observed in satellite images due to meteorological cloud cover. According to webcam views an eruption on 8 November produced a low-level ash plume. The Jakarta Meteorological Watch Office, the webcam, and satellite data detecting sulfur dioxide indicated two explosions on 10 November. The first one, at 0720, generated an ash plume that rose to an altitude of 3.7 km (12,000 ft) a.s.l. The altitude of the second plume, from an explosion at 1600, was unknown. An ash plume on 11 November rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted less than 20 km SW. The next day an ash plume rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted almost 40 km NW.

According to a news article posted on 12 November, more than 5,000 people from seven villages had evacuated their homes in recent days. The article noted that the government had called for an evacuation of people living within a 3-km radius of Sinabung, but people outside of that zone had also been evacuating.

An eruption began at 0126 on 3 November that generated ash plumes up to 7 km a.s.l. (~23,000 ft) and triggered evacuations from communities within 3 km of the volcano (approximately 1,681 residents); the ash plume drifted W. Rumbling sounds that lasted up to 10 minutes long were noted by staff at the Sinabung Observation Post (~8.5 km from the volcano). News agencies reported that this was the second largest eruption since the 24 October event that displaced more than 3,300 people.

The Alert Level was increased from Level II (Watch) to Level III (Alert) at 0300. A second eruption occurred in the afternoon. PVMBG reported that Sinabung had been erupting more frequently and with increasing energy.

PVMBG reported that elevated seismicity, including events of continuous tremor, was ongoing since 29 October. Relatively small ash explosions were also reported prior to the larger events on 3 November. During 29 October-2 November plumes rose to 200-2,000 m above the summit. Gas measurements conducted during 31 October and 1-2 November showed an SO2 flux of 226-426 tons per day; this was a general decrease in emissions. During 31 October ashfall was noted on the SE flank up to 1 km from the summit.

PVMBG reported that an eruption occurred at 1423 on 5 November. This event lasted for 20 minutes and generated an ash plume up to 3,000 m above the crater that drifted SW. Rumbling sounds were also noted by staff at the observation post. Pyroclastic flows were observed at 1431; the flows extended 1 km down the SE flank. No casualties were reported due to the event. The evacuated residents remained displaced on 5 November.

PVMBG reported that after 29 September, the day the Alert Level was lowered to 2 (on a scale of 1-4), seismicity at Sinabung declined but continued to fluctuate through 22 October. White plumes were seen rising 100-300 m from the crater. On 22 October plumes were also grayish and rose 250 m. Vents appeared on the N flank and produced dense white plumes that rose 70 m. On 23 October landslides at two locations were observed, and explosions occurred at 1619 and 1651. Plumes rose from the summit crater and from a fracture formed on 15 October near Lau Kawar. Fog prevented observations for a period after the explosions; once the fog cleared dense gray plumes were observed. A third explosion occurred at 2100. On 24 October an explosion at 0550 generated an ash plume that rose 3 km and caused ashfall in areas S. Another explosion was detected at 0612. According to a news article about 3,300 people that evacuated their homes were mostly from two villages within 3 km of Sinabung, in the Karo district.

Based on information from the Indonesian Meteorological Office, the Darwin VAAC reported that an eruption at 1737 on 26 October generated an ash plume that rose to an altitude of 4.9 km (16,000 ft) a.s.l. At 0700 and 1200 on 27 October a webcam showed an ash plume rising to an altitude of 3.7 km (12,000 ft) a.s.l. and drifting over 35 km NE.

According to the Darwin VAAC, the webcam recording activity at Sinabung showed on 18 September that ash had dissipated. The VAAC also noted that PVMBG confirmed Sinabung was degassing and not emitting any ash. According to a news article, about 6,000 people that had evacuated after the 15 September eruption started to return home on 22 September. The article noted that the volcano was continuing to emit ash.

CVGHM reported that seismicity at Sinabung fluctuated in 2012-2013, including during July-September 2013. During 1-14 September dense white plumes rose 100-150 m above the crater, and at 0255 on 14 September incandescence from the crater was observed. According to news articles an eruption at 0245 on 15 September produced an ash plume and ashfall in Sukameriah (50 km NE), Kutarayat, Kutagugung (16 km SW), and Berastagi (14 km E). About 3,000 people evacuated from areas within a 3-km radius of the volcano, and several flights at Medan's airport (55 km NW) were canceled. CVGHM raised the Alert Level to 3 (on a scale of 1-4).

An eruption at 1203 on 17 September ejected tephra and a dense ash plume that rose higher than the plume from 15 September. According to the Darwin VAAC, a pilot observed an ash plume that rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted 55 km SE. On 18 September a low-level ash plume rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted SE.

Based on information from CVGHM and views through a web camera, the Darwin VAAC reported that during 15-18 September ash plumes from Sinabung rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted W. CVGHM reported a slow rate of inflation during 15-18 September followed by deflation during 19-21 September. Fog mostly prevented visual observations. On 20 September diffuse white plumes rose 30 m above the crater and drifted NE. The Alert Level remained at 4 (on a scale of 1-4).

CVGHM reported that during 8-11 September Sinabung emitted white-to-gray plumes that rose 30-100 m above the crater and generally drifted E. Deformation measurements during 8-14 September showed a slow rate of inflation. Based on analyses of satellite imagery and the CVGHM web camera, the Darwin VAAC reported that on 12 and 14 September ash plumes rose to altitudes of 4.3-4.6 km (14,000-15,000 ft) a.s.l. The Alert Level remained at 4 (on a scale of 1-4).

According to news articles, about 6,000 of the approximately 30,000 people that evacuated the area around Sinabung after the eruption during 29-30 August returned home within a few days because activity had decreased. The Darwin VAAC reported a large explosion on 3 September, based on information from CVGHM. News reports stated that the explosion vibrated homes and trees on the flanks, and generated a 3-km-high ash plume. CVGHM reported that another large explosion on 7 September produced an ash plume that rose 5 km above the crater and drifted SE. Strong vibrations caused by the explosion were detected as far away as 8 km SE.

CVGHM reported that on 28 August Sinabung emitted diffuse white plumes that rose 20 m and showed no signs of increased activity. On 29 August rumbling was heard, prompting authorities to contact and move people living within a 6-km-radius of the volcano. Later that day, an explosion produced an ash plume that rose 1.5 km above the crater, and the Alert Level was raised to 4 (on a scale of 1-4). Media footage of the eruption at one point showed two closely spaced ash plumes from vents near the summit; the ash plumes caused domestic flights to be diverted. The next day a second, more powerful, explosion generated an ash plume that rose 2 km above the crater. The number of people media sources reported had evacuated ranged from 20,000 to 30,000. Ash fell in nearby areas and a strong sulfur odor was reported. Nighttime video showed incandescent material descending the flank of the volcano.

Bulletin Reports

All information contained in these reports is preliminary and subject to change.

This report documents the first confirmed Holocene eruption at Sinabung, beginning on 27 August 2010 (figure 1). Sinabung is an elongated stratovolcano in the Karo plateau of northern Sumatra, Indonesia, ~ 80 km NNW of Toba. By 23 September the Center of Volcanology and Geological Hazard Mitigation (CVGHM) had reported six distinct eruptions (table 1), with another two (12 and 14 September) described by analysts at the Darwin Volcanic Ash Advisory Center (VAAC).

Figure 1. [Photos of the Sinabung eruption during 30 August-3 September 2010.] (top) Plume [on the evening of 3 September deflected by winds down the E flank], but spreading and rising at distance. (bottom) Dual plumes discharging [on 30 August, viewed from the NE], the one at left dropping minor ash in the near-source region. Note portions of antenna, presumably from the instrument telemetry system. The emission of dual plumes appears in photos and videos on the internet. Photo credit to Rahmanto (CVGHM).

Table 1. Date and time of Sinabung explosive eruptions reported by CVGHM as of 22 September 2010.

Although widespread press reports indicated that the last eruption occurred in 1600, this statement is incorrect. CVGHM reported that Sinabung had no radiocarbon dates documented after 1600, but that solfataric activity was observed at the summit in 1912.

An initial phreatic eruption reported by CVGHM occurred on 27 August 2010 following heavy rainfall. Later activity ejected juvenile material and was clearly magmatic. Ash and scoria fell to the E and SE, covering the villages of Sukameriah, Gangpitu, Sigarang-Garang, Sukadebi, and Susuk. On 28 August, only a cloud of sparse white smoke was observed, rising to a height of 20 m.

On 29 August observers heard a rumbling noise. The hazard status was changed to Alert Level 4 (on a scale of 1-4), resulting in authorities relocating people living within a 6 km radius of the volcano. At 1000 on 29 August a continuous eruptive signal was recorded, with amplitudes ranging from 0.5 to 1.5 mm. During the following night of 29-30 August activity became visible, and plumes reached 1,500 m above the crater rim. An explosion several hours later produced a white to medium dark plume. Subsequent explosions sent plumes to heights of ~ 100 m.

Footage of the eruption on 29 August showed two closely spaced ash plumes from vents near the summit. The ash plumes caused domestic flights to be diverted and the local Medan airport was closed. The next day (30 August) a second, more powerful, explosion generated an ash plume that rose 2 km above the crater. Media sources reported that 20,000-30,000 residents had evacuated as ash fell in nearby areas and a strong sulfur odor was reported. Nighttime video showed incandescent material descending an undisclosed flank of the volcano. One news report described six hours of activity on 30 August as "... raining ash and debris across several miles and killing two villagers who suffered respiratory and cardiac problems." Although these fatalities were commonly noted in press reports, the cause of these fatalities (and whether linked to the eruption or coincidental) remained uncertain.

The Darwin VAAC, based on information from CVGHM, reported a large explosion on 3 September. News reports stated that the explosion caused vibrations of homes and trees on the flanks, and generated a 3-km-high ash plume. According to news articles, during 31 August-7 September about 6,000 evacuees had been able to return home because activity had decreased.

CVGHM described the 7 September explosion as the largest of the eruptive episode. It produced a gray-to-black ash plume that rose to a nominal ~ 5 km above the crater and drifted SE. Strong vibrations caused by the explosion were detected as far away as ~ 8 km SE. Andrew Tupper (Darwin VAAC) noted that the plume rose soon after midnight on the 7th and presented huge difficulties for both visual and satellite observations. The 5-km plume altitude estimate came from ground observers (time of observation unknown), but a pilot report noted the altitude as ~ 8 km altitude (FL250, 25,000 feet, over the M300 route). A Volcanic Ash Advisory noted those values and traced the report to CVGHM and observations around 0530 on the 7th (local time and date).

Monitoring campaign. Although there is no continuous monitoring at Sinabung, there is a hazard map to provide guidance to local officials (figure 2). CVGHM installed a near-real-time video monitoring system (see Information Contacts) to assess the volcano's behavior during this active episode. Monitoring included four seismic stations high on the mountain with data telemetered to the observation post. Other monitoring included tilt (from a station at 1,200 m elevation), deformation (electronic distance measuring surveying three reflectors measured from Sukanalu Teran village, 4 km from the summit), and sulfur-dioxide emissions (mini-DOAS, and environmental monitoring using a Drager X-am 7000 in residential areas).

Sinabung, which sits 80 km NNW of Toba caldera, produced its first confirmed historical eruption in August 2010 (BGVN 35:07). We present clarifications on our previous report, some seismic data from the interval 2-4 September 2010 that included large local tectonic earthquakes, episodes of continuous volcanic tremor, and the return of calm after mid-September 2010.

Clarifications. Kus Hendratno (of the Center of Volcanology and Geological Hazard Mitigation, CVGHM) provided additional information about the first figure in our last Sinabung report (BGVN 35:07), which we had captioned as undated.

The upper photo, taken from the SW, showed the second eruption on 3 September (in the evening) and shows a plume he considered to be deflected down the E flank by strong winds blowing down-slope. The lower photo was taken on 30 August from the NE. Hedratno did not know the date that the eruption ended.

In addition, we described the 27 August 2010 eruption as the "first Holocene eruption" in BGVN 35:07. There was an unconfirmed historical eruption in 1881, and there may yet emerge evidence for other Holocene eruptions. Thus, we now prefer to refer to the 27 August eruption as the first confirmed historical eruption.

Additional information about 2-4 September 2010 activity. Table 2 presents some basic data on 2 to 4 September seismicity. These data are but a portion of a 4 September report by Agus Budianto (head of a geophysical team that responded to the crisis). The seismic data reflect both the presence of volcanic earthquakes, earthquakes interpreted as associated with emissions, far tectonic earthquakes, and tremor. The latter continued in all but one 6-hour time slot on the table, and in two cases, 1800-2400 on the 3rd and 0000-0600 on the 4th, tremor reached dominant amplitudes of 50 mm.

An eruption at 0438 on 3 September was accompanied by a roaring sounds and vibrations that were felt up to 8 km SE. A thick black plume erupted up to 3 km above the crater and drifted E. An eruption on the same day during the hours 1759 to 1801 also caused a roaring sound and weak vibrations that were felt up to 8 km away.

Visual observations showed several periods of the eruption; early in the eruption, a black plume soared as high as 1 km above the crater and drifted E. Then, a plume that appeared "clotted" moved approximately 2 km down the E slopes, with most of the ash falling on the E slope. Finally, a plume rose vertically and took the shape of a mushroom.

Electronic distance measurements after the eruption at 1759 on 3 September 2010 showed deflation (up to 4.5 mm).

On 4 September, the weather was clear, and a thick white plume was visible reaching up to 50 m above the crater and drifting as far as 100 m down the E slope.

Activity during mid- to late-September 2010. CVGHM reported a few noteworthy eruptions, emissions, and changes occurred after early September. During 8-11 September observers saw white-to-gray plumes rising 30-100 m above the crater and generally drifting E. Deformation measurements during 8-14 September showed a slow rate of inflation. Based on analyses of satellite imagery and the CVGHM web camera, the Darwin VAAC reported that on 12 and 14 September ash plumes rose to altitudes of 4.3-4.6 km altitude.

During 15 September-21 September 2010, based on information from CVGHM and views through a web camera, the Darwin VAAC reported ash plumes rising to an altitude of 4.3 km and drifting W. CVGHM reported a slow rate of inflation during 15-18 September followed by deflation during 19-21 September. Fog mostly prevented visual observations. On 20 September diffuse white plumes rose 30 m above the crater and drifted NE.

On 22 September a white plume rose as high as 100 m above the crater. The decrease in activity based on visual observations, seismicity, deformation, and SO2 concentration prompted CVGHM to lower the Alert Level to 3 (on a scale of 1-4) on 23 September, where it remained through at least mid-March 2011.

Our previous report on Sinabung (BGVN 36:03) discussed the decreased activity following the 27 August-September 2010 eruption (BGVN 35:07). That was Sinabung's first confirmed Holocene eruption (although there was an unconfirmed eruption in 1881). The decrease in activity since that event prompted Center of Volcanology and Geological Hazard Mitigation (CVGHM) to lower the Alert Level to 3 (on a scale of 1-4) on 23 September, where it remained through at least mid-March 2011. Sinabung is the highest mountain in North Sumatra and sits 80 km NNW of the Toba caldera.

This report includes a more recently available post eruption photo (figure 3). That photo was taken from an aircraft on 13 May 2011 and posted by Johnny Siahaan on Flickr (Siahaan, 2010).

Figure 3. Aerial photo taken 13 May 2011 showing summit area craters and deeply incised upper flanks at Sinabung, as seen in the aftermath of the late 2010 eruption. A thin white plume rises from the summit area. Photo posted by Johnny Siahaan.

This report also includes aspects of the eruption (Siahaan, 2010) during August-September 2010 (BGVN 35:07), including video of the Mt. Sinabung. Johnny Siahaan's video of 30 August 2010 shows a scene with two separate ash plumes rising together (figure 4). The larger plume emitted laterally (almost horizontally) but convection of the hot ash and gasses bent it into the vertical well out over the flank of the volcano. The other plume was initially smaller, escaping from an adjacent but distinct area of the summit, and rising nearly vertically. The two plumes appear to merge at altitude and then bend in the wind. What looks like an older plume in the distance near the beginning of the video rose and was strongly sheared in the wind. The "look direction" of the video was not stated.

In several issues of the Bulletin (BGVN 35:07, 36:03, and 38:04) we described the first confirmed eruption at Sinabung volcano (figure 1), which began 27 August 2010. This report notes ongoing eruptions along with more evacuations, more pyroclastic flows, and plumes as tall as 10 km.

Figure 5. A map centered on Indonesia, showing the location of Sinabung volcano on Sumatra Island near the NW end of the long line of active volcanoes (black triangles) in that country. Sinabung lies 35 km NNW from the nearest margin of the crater lake of Toba, the largest identified volcanic caldera on Earth. Courtesy of U.S. Geological Survey.

The Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that seismicity at Sinabung fluctuated during 2012 and through September 2013. During early September 2013, dense white plumes rose 100-150 m above the crater, and, on 14 September, incandescence from the crater was observed. Although this and several other instances of incandescence from the volcano's crater were reported during this eruption period, no MODVOLC thermal alerts were measured.

An estimated 16,000 people live within 10 km of the Sinabung volcano. Many photos of the volcano during this eruption can be found in an article from The Atlantic (Taylor, 2013). Some of the photos disclosed plumes otherwise little documented.

According to news articles, an eruption at 0245 on 15 September produced an ash plume and ashfalls in the towns of Sukameriah (50 km NE), Kutarayat (location uncertain), Kutagugung (16 km SW), and Berastagi (14 km E). About 6,000 people were evacuated from areas within a 3-km radius of the volcano, and several flights at Medan's airport (55 km NW) were canceled. CVGHM raised the Alert Level to III.

An eruption at 1203 on 17 September 2013 ejected tephra and a dense ash plume that rose higher than the plume seen on 15 September. According to the Darwin VAAC, on 17 September, a pilot observed an ash plume that rose to an altitude of 6.1 km and drifted 55 km SE. On 18 September a low-level ash plume rose to an altitude of 3 km and drifted SE, dissipating later that day. The VAAC also noted that CVGHM had confirmed that Sinabung was degassing but not emitting any ash. The evacuees started to return home on 22 September.

Seismicity at Sinabung declined but continued to fluctuate through 22 October. White plumes were seen rising 100-300 m from the crater. On 29 September 2013, the Alert Level was lowered to II.

On 22 October grayish plumes rose 250 m. Vents appeared on the N flank and produced dense white plumes that rose 70 m. On 23 October landslides at two locations were observed, and explosions occurred at 1619 and 1651 hours. Plumes rose from the summit crater and from a fracture formed on 15 October near Lau Kawar, a lake at the foot of Sinabung. Fog prevented observations for a period after the explosions; once the fog cleared dense gray plumes were observed. A third explosion occurred at 2100 hours. On 24 October at 0550 and 0612 explosions s generated ash plumes, and at least one rose 3 km and deposited ashfall in areas S. Based on information from the Indonesian Meteorological Office, the Darwin VAAC reported that an eruption at 1737 on 26 October 2013 generated an ash plume that rose to an altitude of 4.9 km. At 0700 and 1200 hours on 27 October a webcam showed an ash plume rising to an altitude of 3.7 km and drifting over 35 km NE.

CVGHM reported elevated seismicity including continuous tremor ongoing since 29 October 2013. Relatively small ash explosions were also reported prior to the larger events on 3 November. During 29 October-2 November plumes rose to 200-2,000 m above the volcano's summit. Gas measurements conducted by CVGHM during 31 October and on 1-2 November showed a sulfur dioxide (SO2) flux of 226-426 tons per day; this was a general decrease in emissions compared to those measured routinely during the year In addition, remote sensing data suggested the formation of a new vent sometime between 29 October and 2 November 2013 near the NE summit crater.

During 31 October ashfall was noted on the SE flank up to 1 km from the summit. CVGHM reported that explosions occurred on 3 November at 0126 and 1615, both generating ash plumes up to altitudes of 7 km that drifting W. These triggered evacuations from communities within 3 km of the volcano (~1,681 residents). Rumbling sounds that lasted up to 10 min were noted by staff at the Sinabung Observation Post (~8.5 km from the volcano). News agencies reported that this was the second largest eruption since the 24 October event that displaced more than 3,300 people. The Alert Level was increased from Level II (Watch) to Level III (Alert) at 0300 on the 31st.

Another eruption was reported by CVGHM at 1423 hours on 5 November 2013. This event lasted for 20 minutes and generated an ash plume up to 3,000 m above the crater that drifted SW. Pyroclastic flows were observed at 1431 hours on 5 November that extended 1 km down the SE flank. No casualties were reported.

Based on information from the Jakarta Meteorological Watch Office, webcam data, wind data, and satellite images, the Darwin VAAC reported that on 6 November 2013 an ash plume from Sinabung rose to an altitude of 3 km (figure 2). In addition, a glowing spot was seen near Sinabung's summit.

Figure 6. Sinabung erupts and emits a pyroclastic flow on 6 November 2013. Glowing material appears just below the summit. Hundreds of residents were evacuated to safer areas as the volcano erupted anew following the earlier September 2013 eruptions. Courtesy of Atar/AFP/Getty Images; appeared in Taylor (2013).

The next day an ash plume rose to the same altitude but was not observed in satellite images because of meteorological cloud cover. Webcam images showed an eruption on 8 November that produced a low-level ash plume. The Jakarta Meteorological Watch Office, the webcam, and satellite data detecting SO2 indicated two explosions on 10 November. The first one, at 0720, generated an ash plume that rose to an altitude of 3.7 km. The altitude of the second plume, from an explosion at 1600, was unknown.

An ash plume on 11 November rose to an altitude of 3 km and drifted less than 20 km SW (figure 3). The next day an ash plume rose to an altitude of 3.7 km and drifted almost 40 km NW.

Figure 7. A press photo taken at Sinabung on 11 November 2013. A larger pyroclastic flow seems poised to descend from the summit area behind two smaller, adjacent pyroclastic flows. A narrow columnar cloud hangs over the summit. Courtesy of AP Photo/Dedy Zulkifli; appeared in Taylor (2013).

Based on webcam data and satellite images, the Darwin VAAC reported that during 13-14 November an ash plume from Sinabung rose to an altitude of 3.7 km and drifted almost 150 km NW and W. A pyroclastic flow traveled 1.2 km down the SE flank on 14 November, prompting more evacuations from villages near the base of the volcano.

An explosion observed with the webcam on 18 November 2013 produced an ash plume that rose to an altitude of 7.6 km. About 30 minutes later an ash plume also visible in satellite images rose to an altitude of 11.3 km and drifted 65 km W. Four hours later satellite images showed fresh ash plumes at an altitude of 9.1 km to the W of Sinabung and at an altitude of 4.6 km over the crater. On 19 November the webcam recorded an ash plume that rose to an altitude of 4.6 km over the crater. A news article stated that later that night that an ash plume rose to an altitude of 10 km.

A news article from 20 November noted that volcanologists updated the previous hazard map for Sinabung (see figure in BGVN 35:07). The second-tier disaster-prone area, previously defined as a radius of 2-3 km from Sinabung's crater, was expanded to 4-5 km.

CVGHM reported three explosions from Sinabung on 17 November 2013. The first explosion, at 2024, generated an ash plume that rose 500 m and drifted SW, and a pyroclastic flow that traveled 500 m down the SE flank.

At 2152 hours that day a dense ash plume from an explosion rose 500 m and drifted SW. Incandescent material was ejected 50 m away from the crater. At 2252 an ash plume rose 1 km and drifted SW. At 0704 on 18 November an explosion generated an ash plume that rose 8 km and drifted SW. A pyroclastic flow also traveled 800 m down the SE flank.

On 19 November at 2155 a dense ash plume rose 10 km, drifted SW, and exhibited lightning. Pyroclastic flows again traveled 500 m SE. Multiple explosions on 20 November (at 0240, 0405, 0529, 0619, and 0641) generated ash plumes that rose to heights between 1 and 3.5 km. An explosion at 1716 was detected by the seismic network but cloud cover prevented observations of possible plumes. White plumes rose 100 m on 21 and 23 November, but misty conditions prevented visual observations on 22 November. On 23 November scoria fell in the Sigarang-garang and Desa Kuta villages in the NNE. Two explosions on 24 November, at 0043 and 0232 hours, were detected but not visually observed. Ash plumes rose 8 km and drifted NNE at 0727, rose 1 km at 0812, and rose 3 km at 0855. Since Sinabung's activity continued to increase, CVGHM raised the Alert Level to IV on 24 November. CVGHM noted that residents and tourists were advised not to approach the crater within a 5-km radius. Remaining residents in 17 villages around the volcano were to be evacuated.

CBC.CA.News reported that on 25 November 2013, "6 new eruptions in the morning sent lava and searing gas tumbling up to 1.5 km down the slopes of Mount Sinabung" causing villagers to evacuate. This description apparently refers to pyroclastic flows. Volcanic material erupted as high as 2 km above the crater. The Indonesian National Agency for Disaster Management (BNPB) reported that 17,713 people, out of the 20,270 residents had been evacuated to 31 shelters.

Based on webcam data and wind data, the Darwin VAAC reported that during 28-31 November and 2 December ash plumes from Sinabung rose to altitudes of 3-5.5 km. Ash plumes drifted 150 km W during 30-31 November and 55 km W on 2 December. On 3 December ash plumes rose to an altitude of 8.2 km and drifted W. According to a news report on 2 December, landslides triggered by torrential rain buried houses and killed nine people in Gundaling village, 12 km E. On 4 December an ash plume from Sinabung rose to an altitude of 8.2 km and drifted N. Later that day and during 5-6 December ash plumes rose to altitudes of 3-3.7 km and drifted NW. CVGHM reported that observers in Ndokum Siroga, about 8.5 km away from the volcano, noted gray plumes rising 1 km above Sinabung on 6 December. They also saw grayish-white and dense white plumes as high as 400 m on 7 and 8 December, respectively. Dense grayish-to-white plumes rose 70-200 m on 9 December. White plumes rose 100-150 m above the crater during 10-13 December. Tremor during 6-13 December was recorded continuously, with varying amplitude. The number of low-frequency earthquakes significantly increased on 7 December, and the number of hybrid earthquakes increased the next day. RSAM (real-time seismic amplitude measurement) values of energy steadily increased since 28 November. The Alert Level remained at IV.

In conclusion, seismicity and images of ash plumes and pyroclastic flows suggest that the current eruption of Sinabung volcano began around 14-15 September 2013 and has continued through at least 11 December 2013.

The latest eruption of Sinabung volcano began mid-September 2013; activity through early December 2013 was reported in BGVN 38:09. This report describes the continuing eruption from December 2013 through April 2014, primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) and reports from the Darwin Volcanic Ash Advisory Centre (VAAC). Many videos and photographs also emerged online, some of outstanding information content.

Badan Nacional Penanggulangan Bencana (BNPB — the Indonesian National Agency for Disaster Management) produced a map in 2013 showing disaster-prone areas near Sinabung (figure 1 and table 1). Orange shading shows the highest hazard area, Area III. The S and SE extensions of Area III project downslope, delineating regions and villages with high exposure to pyroclastic- and lava-flow hazards.

Figure 1. 2013 hazard map of Sinabung showing villages within hazard-prone zones, including locations such as the village of Sukameriah located S of the summit (labeled 'Ds. Suka Meriah'). Table 1 translates critical portions of the map key. Courtesy of BNPB; from Carl (2014).

December 2013-January 2014. Based on webcam images, the Darwin VAAC reported that on 22 December an ash plume from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 55 km W. During 23-24 December ash plumes recorded by the webcam rose to an altitude of 3 km (10,000 ft) a.s.l.

PVMBG reported that seismicity at Sinabung increased during 21-26 December and indicated rising magma and lava-dome growth. Observers in Ndokum Siroga, about 8.5 km away, noted dense white plumes rising 70-1,200 m above the crater. Roaring was also periodically heard. A lava dome in the North Crater, visible on 24 December, was 56 m high and 210 m wide. During 25-26 December plumes were white and gray, and rose 300-400 m above the crater. On 26 December the lava-dome volume was estimated to be over 1 million cubic meters, with a growth rate of 3.5 cubic meters per second. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

On 30 December Badan Nacional Penanggulangan Bencana (BNPB) reported that the number of displaced people reached 19,126 (5,979 families). They also noted that activity at Sinabung had increased. Collapsing parts of the lava dome generated block-and-ash flows as well as pyroclastic flows which traveled as far as 3.5 km down the SE flank. Explosions and pyroclastic flows generated ash plumes that rose at least 6 km above the crater.

Figure 2. A woman carrying her daughter in an agricultural plot near Sinabung as an ash plume rose and pyroclastic flows descended the flanks on 4 January 2014. Photo by Ifansasti (2014).

At 1600 (UTC) (2300 local) on 4 January 2014, MODVOLC satellite thermal alerts were measured over Sinabung for the first time in at least the last 10 years. (The MODVOLC system was described in the 1980's and an online version started during 2000-2001, although some similar thermal databases now span on the order of 4 decades (Ramsey and Harris, 2011; Wright and others, 2004)). Lava effusion was high, resulting in thermal alerts during much of January 2014. From the time of that first alert, nearly daily to weekly alerts were measured through May 2014.

During 4-5 January pyroclastic flows were recorded 426 times. On 5 January the number of hybrid earthquakes increased, indicating lava-dome growth, and pyroclastic flows traveled 1.5-4.5 km SE. On 7 January ash plumes rose 1-6 km and drifted SW, and pyroclastic flows continued to travel 1.5-4.5 km SE. The village of Payang, ~4.6 km S of Sinabung's summit, was blanketed by ash on 7 January 2014 (figure 3).

Figure 3. The village of Payung (~4.6 km S of Sinabung's summit) as ash falls during the eruption of Sinabung on 7 January 2014. Image courtesy of Martin (2014); photography by Ulet Ifansasti/Getty Images.

A pyroclastic flow photographed on 10 January appears in figure 4. BNPB reported that the number of hybrid earthquakes decreased on 11 January and volcanic earthquakes increased. Amid these January eruptions aAsh plumes rose 1-5 km and drifted W, and pyroclastic flows traveled 1-4.5 km SE and 1 km E. Several villages in the Namanteran district reported ashfall. On 16 January, satellite imagery showed a white ash plume underlain by previous deposits of gray pyroclastic flows (figure 5). Around this time, the number of refugees reached over 22,000 persons.

Figure 4. Pyroclastic flows traveling down Sinabung's S flank during an eruption on 10 January 2014. This photo was taken from Berastepu village in Karo district (~4 km SE of volcano summit). Courtesy of Bracken (2014), with caption information from REUTERS/Beawiharta.

Figure 5. The Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite collected this natural-color image of an ash plume from Sinabung on 16 January 2014. Frequent collapses from the unstable lava dome at the volcano's summit created pyroclastic flows that have traveled at least 4.5 km down the volcano's flanks. The SE margin of these flows are just visible to the lower right of the plume. Courtesy of NASA Earth Observatory. Image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team. Caption by Robert Simmon.

A number of images of the eruption of Sinabung volcano during the second week of January 2014 are available on the Photovolcanica website (Roscoe, 2014). James Reynolds captured some remarkable videos of pyroclastic flows at Sinabung on 21 January 2014 (Earth Uncut TV, 2014; Vervaeck, 2014). Those videos showed explosions that often initiated the pyroclastic flows. As the flows moved downslope, they rapidly formed turbulent, ash-laden currents comprising the bulk of the flow volume (see Figure 3). An image of the S flank of Sinabung taken on 14 January shows lava flows erupting from the summit (figure 6).

Figure 6. Sinabung volcano on 14 January 2014 as it erupts a small plume and a lava flow that traveled down the volcano's S flank, as seen from Kuta Tengah village. Note the sinuous gulley (shaded depression) running downslope just to the right (E) of the lava flows; this is also a prominent landmark in figure 9. Courtesy of India Times (2014).

On 31 January 2014 Sinabung continued to effusively erupt viscous lava, further contributing to both the growth of the lava dome and the lava flow that descended the SE flank. The depression on the SE side of the volcano was mostly been filled by the lava flow, prompting concerns that pyroclastic flows lacked confinement and might take other paths to the S or E.

February 2014. On the morning of 1 February 2014 the lava dome collapsed and created one or two pyroclastic flows. As a result, 17 people (mostly students) died. All known fatalities occurred in Sukameriah village ('Ds. Suka Meriah,' figure 1). That village sits just over 3 km S of the summit, thus well within the 5-km-exclusionary zone. The resulting expanse of hot deposit generated a series of narrow spinning vortices ('twisters') of rising air and ash, that with height joined a rising plume (figure 7).

Waning trend. According to CVGHM, during 2-4 February 2014 no significant explosions or pyroclastic flows seemed to have occurred. Activity showed an overall decreasing trend. The number of seismic events related to the rise of new magma (hybrid earthquakes and tremor) had generally decreased over the preceding weeks. This corresponded to what was observed visually (when weather permitted clear views). Occasional medium-sized explosions and dome collapses produced pyroclastic flows that reached up to 3 km in length at 1350 on 3 February and at 0750 on 4 February.

Based on webcam images, Indonesian Met office notices, wind data, and ground reports, the Darwin VAAC reported that during 12-13 and 15-18 February ash plumes from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 25-95 km N, NE, and E.

During 15-23 February 2014 the eruption continued without significant changes, but with progressively decreasing activity. CVGHM noted the slow extrusion and gradual enlargement of the lava effusing from the summit vent and onto the S slope. Occasional rockfalls, ash emissions, and minor pyroclastic flows occurred as well. The erupted lava was determined to be andesite, typical of many stratovolcanoes in subduction settings.

March 2014. Based on wind data, webcam images, and satellite images, the Darwin VAAC reported that during 25 February-1 March and 3-4 March ash plumes from Sinabung rose to altitudes of 3-4 km a.s.l. and drifted 25-55 km E, NE, N, NW, W, and SW. Darwin VAAC also reported that during 4-7 and 9-11 March ash plumes from Sinabung rose to 3.7-4 km a.s.l. and drifted W and SW. During 6 and 9-11 March ash plumes drifted 35-165 km SW and W.

PVMBG described activity at Sinabung during 8-15 March based on observations from a post in the Ndokum Siroga village, 8.5 km away. Dense white plumes rose from the lava dome daily, as high as 1 km on most days; plumes rose 2 km on 12 March. Incandescent material originating from various parts of the lava dome traveled up to 2 km S and SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome increased. Sulfur dioxide emissions varied between 300 and 598 tons per day. Observations on 13 March showed that lava from the dome had flowed 2.4 km downslope.

On 15 March 2014, Sinabung was still at Alert Level 4 (the highest level). During 15-22 March 2014, there was a declining trend in the RSAM (real-time seismic amplitude measurement).

The volcano continued to be active on 18 March 2014 with no significant changes, but an overall decreasing trend. Lava effusion fed the S-flank lava lobe which had been mainly growing along its E side. No significant pyroclastic flows occurred, only frequent smaller rockfalls. Small ash plumes continued to be regularly visible on satellite imagery. The 18 March report indicated that seismicity decreased overall and hybrid earthquakes had disappeared. This suggested to the authors that pressure and magma supply rate had dropped significantly and that the eruption could be ending in the near future.

Based on webcam images, the Darwin VAAC reported that on 29 March an ash plume from Sinabung rose to an altitude of 4.3 km (14,000 ft) a.s.l. Meteorological cloud cover prevented satellite views.

On 30 March 2014, CVGHM reported a slowly decreasing trend in activity, with little variation over the preceding weeks. The viscous lava lobe remained weakly sustained and continued to grow very slowly. An intermittent steam and an occasional ash plume often rose to ~4.2 km a.s.l. No new pyroclastic flows occurred. During 23 March-8 April dense white plumes rose at most 1.2 km above the lava dome. Lava had traveled 2.5 km down the flanks as of 6 April and was incandescent at various locations. Incandescent material originating from the edges of the lava dome and flow traveled up to 2 km S and 500 m SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome decreased. Sulfur dioxide emissions varied but were relatively insignificant. Based on decreasing seismicity, deformation, and SO2 gas flux, CVGHM lowered the Sinabung Alert Level from 4 to 3 on 8 April 2014.

Flow paths into April 2014. Figure 8 shows two satellite images of Sinabung, the upper taken on 7 June 2013 (before the eruption) and the lower taken on 6 February 2014 (during the current eruption). The path of the pyroclastic and lava flows on the SE flank shows the extent of the devastated area and the orientation of other images (figures 6 and 9). Ashfall coated nearby villages and the flanks, as well as the coffee, chili pepper, and other types of plantations clustered at the foot of the volcano.

Figure 8. (Top) Pre-eruption Sinabung image acquired by Landsat on 7 June 2013; much of the surrounding landscape was covered by dark green forests. (Bottom) An image acquired on 6 February 2014 by the Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite. This is a natural-color image of an ash plume, a light gray apron of pyroclastic flow deposits, and broad scale ash fall coating much of the region. Frequent collapses from the unstable lava dome near Sinabung's summit created pyroclastic flows that traveled at least 4.5 km from the summit. NASA Earth Observatory images by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team and Landsat data from the U.S. Geological Survey. Caption by Robert Simmon and Adam Voiland.

CVGHM prepared an image (figure 9) of the path along which lava and pyroclastic flows traversed down the S side of Sinabung, delineating the extent of the lava flows at various dates from 31 January through 6 April 2014. On 6 April 2014 the lava flow was 2.5 km from the volcano summit. The image of 6 February 2014 (figure 8) revealed that pyroclastic flows had gone ~4 km from the summit of Sinabung. Some of those pyroclastic-flow deposits appear outboard and below the lavas at the bottom of figure 9.

Figure 9. This 6 April 2014 photograph of the S flank of Sinabung was annotated with dates by CVGHM (in Indonesian) to mark the advance of lava during 31 January-6 April 2014. The annotations include such features as flow margins and fronts ('lidah lava' means lava tongue). Taken from the CVGHM weekly report of 8 April 2014.

A report from CVGHM dated 10 April 2014 indicated that lava had recently extruded slowly, feeding a thick lobe on the S flank. The effusion rate had declined, hybrid earthquakes disappeared, and rockfall-induced seismicity decreased. Owing to these recent decreases in the intensity of activity, on 10 April authorities decreased the alert status from the Level 4 to 3 (on a scale of 1-4). People from some of the evacuated areas (to the E and NE) were allowed to return to their homes where they began the process of cleaning up the ash (of unstated thickness). Only the areas remaining off limits were within 3 km radius (eg., Sukameriah) and the SE sector village Berastapu (figure 1).

The lava lobe descending from the summit was considered by CVGHM to represent a large unstable mass draped onto the steep slope of the volcano. They acknowledged the risk of a sudden failure that could potentially result in a devastating pyroclastic flow. A pyroclastic flow did occur on 17 April 2014 at 1740, triggered by a partial collapse of the steep lava tongue. The flow was relatively small and only reached the then depopulated area at the base of the volcano.

Based on webcam images, satellite images, and wind data, the Darwin VAAC reported that on 22 April an ash plume rose to an altitude of 3.7 km and drifted almost 40 km W. MODVOLC thermal alerts were measured on 21 April 2014 at 1540 UTC and on 26 April 2014 at 1855 UTC.

Geophysical and geochemical plots. Figures 10 and 11 summarize measurements made and provided by CVGHM; figure 10 plots seismic signals measured from 7 November 2013 to 8 April 2014, and figure 11 plots various geochemical fluxes from1 September 2013 to 8 April 2014.

Figure 10. Plots showing on the y-axis the daily number ('jumlah') of various seismic events measured at Sinabung volcano for the period 7 November 2013 (07/11/2013) to 6 April 2014 (06/04/2014). The common x-axis values depict time, with dates shown for 10-day intervals, using the format 'dd/mm/yyyy'. The seismic types include: 'letusan'-seismically-detected eruptions; 'guguran'-avalanche signals, which correlated with the instability of the lava dome; 'hybrid' earthquakes—associated with growth of the lava dome; and 'VA'-deep volcanic earthquakes, indicating the persistence of a relatively small pressure due to intrusion of magma. Although not shown, CVGHM also measured low-frequency and shallow-volcanic earthquakes and tremor. Courtesy of CVGHM.

The deep volcanic ('VA') and hybrid earthquakes were among the earliest to show clear escalation, with the latter the most sustained. As seen on figure 10, all seismic data, except that associated with avalanches, decreased dramatically after mid-February 2014.

Figure 11 shows in the upper panel, the same seismic peak ('Letusan,' seismically detected eruptions) seen in the previous figure, an interval of high values measured in late December and especially prominent during early to mid-January. In the 2nd panel from the top, SO2 flux, there is a gap in data during the time of the eruption, due at least in part to the challenge of obtaining meaningful measurements in ash-choked plumes. Pronounced peaks occurred in available SO2 flux measurements during the periods 11-18 January and ~mid to late February 2014, with data gaps in their midst, probably for the same reasons just mentioned. Later and earlier measurements yielded much lower fluxes.

The 3rd panel down plots hot-spring-water temperatures ('suhu air panas'), which showed but gradual changes on the order of 0.5°C increase overall. The 4th and 5th panels down plot CO2 and H2S, respectively (in percent by volume) for the same area. Both those measurements display similar patterns. They lack data from January, around the time the eruption, thwarting direct comparisons to the eruption. In addition, CVGHM measured and reported deformation nearby Sinabung from tiltmeters and electronic distance measurement (EDM) equipment (not shown here). They also employ a webcam to monitor the volcano in clear weather.

Figure 11. Daily number of explosion earthquake ('Letusan') and various geochemical fluxes and concentrations measured at Sinabung volcano on a common x-axis scale for the period from 1 September 2013 to 8 April 2014 (in figure as 01/09/2013 to 08/04/2014; i.e., dates in the format 'dd/mm/yyyy'). The measurements indicated by the heading labels for each graph include: 'letusan' — eruption earthquakes per day; SO2 flux in tons/day; 'suhu air panas'—water temperature of the hot springs area in District Payung at the S foot of Sinabung in °C; and hot spring CO2 and H2S there in percent by volume. Courtesy of CVGHM.

Geological Background

Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical, 2460-m-high andesitic-to-dacitic volcano is at the southern end of the four overlapping summit craters. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Sinaboeng | Sinabun

Craters

Feature Name

Feature Type

Elevation

Latitude

Longitude

Sigala, Batu

Crater

Photo Gallery

The conical Sinabung volcano, seen here from the east, rises above farmlands on the Karo Plateau. Gunung Sinabung contains four summit craters, the southernmost of which is the youngest. Many prominent lava flows appear on the flanks of the volcano. No confirmed historical eruptions are known from Gunung Sinabung.

Photo by Tom Casadevall, 1987 (U.S. Geological Survey).

Sinabung volcano, seen from Gurukinayan village on the south, shows prominent lava flows on its flanks and a dramatic summit spine. The summit of Gunung Sinabung is much less frequently visited than neighboring Sabayak volcano to the NE.

Photo by S. Wikartadipura, 1982 (Volcanological Survey of Indonesia).

Sinabung volcano, seen here from Tigapancur village, is a prominent conical stratovolcano that rises above the Karo Plateau in NW Sumatra. Levees of massive lava flows (left-center) are prominent on the flanks of the volcano. No confirmed historical eruptions are known.

Photo by S. Wikartadipura, 1982 (Volcanological Survey of Indonesia).

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).